This invention relates generally to improved osteotomy fixation, and more particularly to a unique fixation bracket, and a method for using it in a pelvic ostectomy. A preferred manner of practicing the invention is described in conjunction with veterinary surgery on a canine pelvis.
Hip dysplasia is a painful and frequently disabling condition of instability between the acetabulum and the femoral head. It usually results from insufficient formation of the acetabulum, which is the cup-shaped socket that receives the femoral head. As the hip is a load-bearing joint, instability in the positional relationship of the acetabulum and femoral head frequently results in further injury to surrounding tissue.
Surgical techniques for correcting hip dysplasia have been suggested, notably the pelvic osteotomy. In that procedure, an acetabular segment is rotated to allow the underformed acetabulum better to "cover" the femoral head. Fixation plates are frequently used to fix the angular position of the rotated acetabular segment relative to the pelvis. Unfortunately, numerous complications arise as a result of this popular procedure, primarily due to loss of fixation and pelvic canal constriction. The more prevalent loss of fixation problem may leave the patient in worse condition than before the surgery, as the pelvic osteotomy is an invasive procedure requiring three pelvic incisions, the removal of one pelvic section and the separation and rotation of another. The chronic bowel and urinary tract problems that result from constriction of the pelvic canal are, at best, uncomfortable and, at worst, injurious. When coupled with the neuroses that frequently accompany such invasive surgical techniques, these complications render the procedure, as it is conventionally practiced, seriously flawed.
Alternatives to the practice of pelvic osteotomies to correct hip dysplasia have been proposed. Notably, a less invasive osteotomy that lengthens (and optionally torses) the biomechanical femoral neck will, in many cases, correct hip dysplasia without resort to a pelvic osteotomy. It has also been discovered that improved results obtain from a pelvic osteotomy when it is performed in combination with such a femoral neck-lengthening osteotomy. Such a method is described in my co-pending application, Ser. No. 06/946,863, filed Dec. 29, 1986, for "0steotomy Method for Biomechanical Femoral Neck-Lengthening and Torsion." Nevertheless, there will be circumstances that demand the continued use of the pelvic osteotomy procedure.
Loss of fixation results from the use of narrow fixation plates that, when subjected to the shear and torque forces incident to acetabular segment rotation, tend to fracture, bend or loosen. The failure of fixation plates to counteract these torsional forces permits loss of fixation and uncontrolled rotation of the acetabular segment, and retards the bone healing process. A fixation device that eliminated these fixations problems would significantly improve the prospects for a successful pelvic osteotomy.
Constriction of the pelvic canal results from rotation of the acetabular segment. When the acetabular segment is rotated on its median axis, the depending portions thereof move medially in the direction of the opposite ilium. Depending upon the degree of rotation, the resulting constriction of the pelvic canal ranges from negligible to occlusive. Even when appreciated, the problem of pelvic canal restriction has heretofore been unavoidable because conventional fixation plates do not allow for the securing of bone sections that are offset from one another. A fixation bracket and improved procedure that allow both rotation and offsetting of the acetabular segment relative to the pelvis would permit stabilization of the coxofemoral joint without the problematic restriction of the pelvic canal.
The present invention discloses a fixation bracket and an improved pelvic osteotomy technique by which both the loss of fixation and canal constriction problems may be avoided.
A principal object of the invention is to provide a fixation bracket that is not subject to fracturing, bending or loosening when used in a pelvic osteotomy procedure.
Another important object of the invention is to provide a fixation bracket, the installation of which permits the securing of a rotated acetabular segment to the pelvis under axial compression.
A further object of the invention is to provide a bracket of the type outlined that is easily adaptable to a range of acetabular segment rotation requirements.
According to a preferred embodiment of the invention, a fixation bracket is described that includes a pair of generally planar fixation plates joined rigidly at their marginal edges in predetermined relative-angular and -positional relationship. Each plate is intended for securement by screws to one of the to-be-joined pelvic sections, which consist of a cut, rotated and offset acetabular segment and the ilium section from which it has been separated. The angle between the planes of the fixation plates is fixed such that median axes of the plates are offset (laterally) from one another. This offset provides the necessary compensation for the rotation that would otherwise result in the constriction of the pelvic canal. The stair-stepped offset between the plates relative to the line of intersection of their planes serves the purpose of generally conforming the bracket to the ilium's natural incline in order to maximize securement thereto (and to the sacrum, if desired).
In its preferred embodiment, the fixation bracket takes the form of opposite, stair-step-shaped plates, having parallel surfaces, joined at their marginal edges by a normally disposed, planar web of similar thickness, also having generally parallel surfaces. Each plate has three elongate holes, approximately equally spaced across the two-dimensional expanse of the plate. The long axis of the elongate holes is perpendicular to the plates' joined marginal edges. In an area at the end of each hole nearer the web, the plates are beveled to provide an inclined surface. When securing screws are tightened, these inclined surfaces provide, by wedging action against the underside of the screws' heads, relative movement between the bracket and the two ilium sections to which it is being secured, thereby urging the ilium sections toward each other normal to the plane of the cut.
In a modification to the preferred embodiment of the invention, a fixation bracket is described in which the web member takes the form of an isthmus. The isthmus is made with a sufficiently small cross section that it may be altered (pre- or intra-operatively) to adjust the angle between the two plates.
According to the preferred method of practicing the invention, an acetabular segment is both rotated and offset to increase the effective width of the pelvic canal. The method principally involves (1) removing the pubic ramus from the pelvis, (2) cutting through the tuber ischii parallel with the sagittal plane, (3) cutting through the ilium in the transverse plane just caudal to the sacro-iliac joint, (4) rotating the thus created, free ilium section on its median axis, (5) offsetting the section relative to the pelvis and (6) fixing the sections (using the fixation bracket described herein).
Fixation of the remaining free end of the rotated and offset ilium section is, in the preferred method, accomplished by conventional wiring. Fixation will be understood to include bone-grafting around the area of the second cut, as by use of the pubic ramus previously removed, to promote osteosynthesis.
Use of the preferred embodiment of (or the modification to) the device of this invention, in conjunction with the improved osteotomy method that includes offsetting of the acetabular segment before fixing it, enables the practice of a pelvic osteotomy without the complications described above. In particular, loss of fixation and pelvic canal restriction may be prevented, enabling the successful stabilization of the coxofemoral joint.
These and other advantages and features of the invention will be come more fully apparent when the detailed description below is read with reference to the accompanying drawings.